SPHINCS+

Stateless hash-based signatures

SPHINCS+

SPHINCS+ is a stateless hash-based signature scheme, which was submitted
to the NIST post-quantum crypto project.
The design advances the SPHINCS signature scheme, which was presented at EUROCRYPT 2015.
It incorporates multiple improvements, specifically aimed at reducing signature size.
For a quick overview of the changes from SPHINCS to SPHINCS+
see the blog post by Andreas Hülsing.
The submission proposes three different signature schemes:

SPHINCS+-SHAKE256

SPHINCS+-SHA-256

SPHINCS+-Haraka

These signature schemes are obtained by instantiating the SPHINCS+ construction
with SHAKE256, SHA-256, and Haraka, respectively.